Energy decoupling of closely spaced radar antenna horns



Aug. 29, 1961 J. c. CACHERIS 2,998,502

may DECOUPLING 0F CLOSELY SPACED RADAR ANTENNA HORNS Filed Oct. 3, 1951 INVENTOR. JOHN C. GACHERIS ATTORNEYS United States Patent 2,998,602 ENERGY DECOUPLING 0F CLOSELY SPACED RADAR ANTENNA HORNS John C. Cacheris, Washington, D.C., assignor to the United States of America as represented by the Secretary of the Navy Filed Oct. 3, 1951, Scr. No. 249,609 4 Claims. (Cl. 343-775) (Granted under Title 35, US. Code (1952), see. 266) The present invention relates generally to an improvement in radio antennae, and is more particularly concerned with a means for decoupling closely spaced radio antennae feeds.

In the art of locating or tracking objects by means of transmitting radio waves and receiving the echos thereof as reflected from the objects, it has been found desirable in certain applications to utilize a plurality of closely spaced antenna energy feeds for directionally transmitting and/or receiving the radio waves. An example of such a system utilizing an antenna having two closely spaced energy feeds cooperating with a parabolic energy reflector to transmit radio waves and to receive the echos thereof directionally is described in the application of Fred S. Atchinson, Serial Number 294,113, filed on June 17, 1952, now abandoned. When utilizing two closely spaced energy feeds for simultaneous transmission, a portion of the energy transmitted from each of the feeds may couple into the other feed and distort the signal transmitted therefrom. Similarly if two such feeds are used for alternate energy reception, wherein each feed is sequentially blocked and opened to energy reception alternately with the other feed, a portion of the energy received by the antenna may enter the blocked feed, be reflected by the block back out of the feed, and then couple into the open feed to distort the signal there received. The disadvantages of such energy coupling and resultant signal distortions are apparent, and it is therefore an object of the present invention to provide an antenna structure enabling the use of a plurality of closely positioned energy transmitting and/or receiving feeds by minimizing or substantially reducing the energy coupling that would be normally had therebetween. Other objects and advantages of the present invention will be apparent to those skilled in the art from a consideration of the following detailed description thereof, made in conjunction with the accompanying drawings in which:

FIG. 1 is a front view of an antenna embodying the present invention; and

FIG. 2 is a side view of the antenna shown in FIG. 1.

Referring to the drawings, numerals and 11 indicate two energy feeds generally, and are here shown as the transmission or reception ends of two waveguides 12 and 13 respectively, as are commonly employed in the transmission or reception of electromagnetic microwaves. In order to provide for directional transmission and/or reception of energy, the feeds 10 and 11 may be directed toward and cooperate with a parabolic reflector 16 or the like.

In order to minimize and substantially reduce the en- 'ergy coupling that would normally exist between the two closely spaced feeds 10 and 11, as previously indicated, a plate of electromagnetic microwave energy absorbing material 17 is placed between and may be supported by the ends 12a and 13a of the waveguides 12 and 13 respectively, and is positioned to extend a substantial distance beyond the ends of the waveguides. This plate functions to interrupt and substantially to prevent the flow of the energy between the ends of the waveguides by absorption of that energy that would normally couple therebetween. It has been found that electrically semiconductive material is suitable for performing the decoupling function of the plate 17-, and by the term electrical semi-conductive material in this specification and the appended claims is meant that type of material which has a conductivity and particularly surface conductivity intermediate in value between materials classed as electrical conductors and those classed as electrical insulators, such as metalized glass and carbon impregnated fabric or Bakelite.

In accordance with the present invention, there is therefore presented an antenna comprising two receiving and/or transmitting energy feed spaced closely together and having a plate of energy absorbing material interposed between the ends thereof for substantially decreasing and minimizing energy coupling between the feeds. Thus, the simultaneous or alternate directional transmission or reception of electromagnetic microwave energy in two slightly divergent directions from one antenna is enabled through the close positioning of the two feeds, substantially little distortion of received or transmitted signals being suifered, as normally would be caused by energy coupling between the closely spaced feeds in the absence of the energy absorbing plate.

Although herein specifically described in its application to a two directional antenna having two closely spaced energy feeds, it is apparent that the present invention is equally applicable to an antenna employing more than two feeds for more than two directions of energy transmission or reception, wherein it would be merely necessary to provide the energy absorbing plate 17 with a suitable shape for appropriately shielding each feed from the others, as would be apparent to one skilled in the art; or a plurality of energy absorbing plates may be provided for accomplishing the same effect. Other modifications of the exemplary embodiment herein described within the spirit and scope of the present invention as defined by the appended claims will be apparent to those skilled in the art, and are within the contemplation of the present patent.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. An antenna for electromagnetic microwave energy transmission or reception comprising two closely spaced waveguide feeds for eifecting their respectively individual energy radiations or receptions, and a plate of electromagnetic microwave energy absorbing material interposed between and extending beyond the ends of said feeds, said plate comprising a material chosen from the group consisting of metalized glass, carbon impregnated fabric, and carbon impregnated Bakelite, thereby enabling the close positioning of said feeds without excessive energy coupling therebetween.

2. An antenna for electromagnetic microwave energy transmission or reception comp-rising two closely spaced waveguide feeds for effecting their respectively individual energy radiation or receptions, and a plate of electromagnetic microwave energy absorbing material interposed between and extending beyond the ends of said feeds, said energy absorbing material being an electrical semiconductor, thereby enabling the close positioning of said feeds without excessive energy coupling therebetween.

3. An antenna for radio energy transmission or reception comprising two closely spaced energy feeds for effecting their respectively individual radiations or receptions, and a plate of radio energy absorbing material interposed between and extending beyond the ends of said feeds, said energy absorbing material being an electrical semiconductor, thereby enabling the close positioning of said feeds without excessive energy coupling therebetween.

4. An antenna for radio energy transmission or reception comprising two closely spaced energy feeds for effecting their respectively individual radiations or receptions, and a plate of energy absorbing material interposed between and extending beyond the ends of said waveguides, thereby enabling the close positioning of said waveguides without excessive energy coupling therebetween.

References Cited in the file of this patent UNITED STATES PATENTS King Apr. 16, 1940 Linder July 1, 1947 Tawney Feb. 24, 1948 Fernsler Mar. 29, 1949 Tawney May 10, 1949 

